Due to loss of hearing, a deaf person cannot hear external sounds, which brings about much inconvenience for the deaf person. For example, in the presence of a whistle from a nearby motor vehicle on the road, a sound of a doorbell in a house or calling from someone, the deaf person cannot hear the sounds at all, let alone recognize from which direction the sounds come, and thus the deaf person cannot respond accordingly in time. Therefore, an insecurity factor is present.